This invention relates to a circuit arrangement for supplying a lamp, provided with a DC/DC converter comprising
a first input terminal and a second input terminal for connection to a power supply source supplying a DC voltage, PA0 a transformer having a primary winding and a secondary winding, PA0 a first branch interconnecting the input terminals and comprising a series arrangement of a switching element and the primary winding, PA0 a control circuit coupled to a control electrode of the switching element for generating a control signal so as to render the switching element high-frequency conducting and non-conducting, PA0 a second branch comprising a series arrangement of a first unidirectional element and a first capacitive element and connecting a first end of the secondary winding to a second end, and PA0 a first output terminal and a second output terminal for connecting a load circuit comprising the lamp.
The invention also relates to an illumination unit comprising such a circuit arrangement and a load circuit which is coupled to the output terminals of the circuit arrangement and comprises a lamp.
A circuit arrangement as described in the opening paragraph is known from WO 97/02722. The known circuit arrangement comprises a DC/DC converter of the flyback type and is very suitable for supplying, for example, high-pressure discharge lamps. The output voltage supplied by the DC/DC converter consists of the sum of the power supply voltage and the voltage across the first capacitive element. If the desired value of the output voltage is relatively high, for example, because the lamp to be supplied has a high operating voltage, this means that, at a given value of the amplitude of the power supply voltage, the voltage across the first capacitive element must also be relatively high. A first drawback thereof is that the first capacitive element must be dimensioned for such a high output voltage, so that the first capacitive element is relatively voluminous and expensive. A second drawback is that the amount of energy dissipated during charging and discharging of the parasitic capacitance between the ends of the secondary winding is relatively large.